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Methyl orange

Methyl orange
IUPAC name 4-dimethylaminoazobenzene-4'-sulfonic acid sodium salt
Other names p-dimethylamino-azobenzenesulfonic acid
CAS number 547-58-0
SMILES CN(C)c1ccc(cc1)N=Nc2ccc(cc2)S(=O)(=O)O[Na]
Molecular formula C14H14N3NaO3S
Molar mass 327.33 g/mol
Density 1.28 g/cm3, solid
Melting point

>300 °C (Not precisely defined.)

Boiling point


Solubility in water Soluble in hot water
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Methyl orange is a pH indicator frequently used in titrations.

It is often chosen to be used in titrations because of its clear colour change. Because it changes colour at the pH of a mid-strength acid, it is usually used in titrations for acids. Unlike a universal indicator, methyl orange does not have a full spectrum of colour change, but has a sharper end point.

Indicator colours

Methyl orange (pH indicator)
below pH 3.1 above pH 4.4
3.1 4.4
Methyl orange in xylene cyanole solution (pH indicator)
below pH 3.2 above pH 4.2
3.2 4.2

In a solution becoming less acidic, methyl orange moves from red to orange and finally to yellow with the reverse occurring for a solution increasing in acidity. It should be noted that the entire colour change occurs in acidic conditions.

In an acid it is reddish and in alkali it is yellow.

Other Indicators

  • Modified (or screened) methyl orange, an indicator consisting of a solution of methyl orange and xylene cyanol, changes from gray to green as the solution becomes more basic.
  • A number of other common indicators are tabulated in the article on pH indicators.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Methyl_orange". A list of authors is available in Wikipedia.
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